Adjust styles to match the design system (#11118)

### What problem does this PR solve?

- Modify and adjust styles (CSS vars, components) to match the design
system
- Adjust file and directory structure of admin UI

### Type of change

- [x] Refactoring

web/src/services/admin.service.d.ts

@@ -32,6 +32,7 @@ declare module AdminService {
   };
 
   export type UserDetail = {
+    avatar?: string;
     create_date: string;
     email: string;
     is_active: '0' | '1';
@@ -46,6 +47,7 @@ declare module AdminService {
   };
 
   export type ListUserDatasetItem = {
+    avatar?: string;
     chunk_num: number;
     create_date: string;
     doc_num: number;
@@ -58,6 +60,7 @@ declare module AdminService {
   };
 
   export type ListUserAgentItem = {
+    avatar?: string;
     canvas_category: 'agent';
     permission: 'string';
     title: string;